The use of flexible coatings to protect surfaces from damage whether by physical or chemical means is well known. Such surface coatings will be expected to provide a decorative appearance when used internally or externally.
The invention provides copolymer emulsions suitable for incorporation in surface coatings. These coatings are sufficiently flexible to provide bridging across any cracks that may develop in the substrate due to movement and the products of the invention are effective even at relatively low temperatures. They possess the necessary combination of water retention and permeability properties.
General description of the invention
The invention provides a copolymer emulsion comprising a core/shell structure in which the core comprises by weight:
i) from about 10% to about 60% of vinyl C1 to C4 alkanoate, PA1 ii) from about 10% to about 30% of C2 to C4 alkylene, PA1 iii) from about 1% to about 10% of alkyl (C2 to C12) acrylate PA1 iv) from about 10% to about 40% of vinyl esters having the general formula R.sub.1 R.sub.2 R.sub.3 CCOOCHCH.sub.2 wherein R.sub.1 R.sub.2 and R.sub.3 are each alkyl groups having at least one carbon atom and R.sub.1 +R.sub.2 +R.sub.3 have from 6 to 9 carbon atoms (vinyl versatates), PA1 v) from about 0.1% to about 5% by weight of a vinyl silane and PA1 vi) the shell, which comprises from about 5% to about 40% by weight of the total copolymer solids, comprises vinyl C1 to C4 alkanoate at a level of at least 80%. PA1 i) 3% to 35% dry weight copolymer solids, PA1 ii) 5% to 35% aqueous phase including water present in emulsion, PA1 iii) 5% to 55% filler, and PA1 iv) 5% to 30% pigment PA1 i) Tensile strength/elongation: An emulsion sample centrifuged to remove air was drawn down to a 0.63 mm film on a ptfe coated glass plate and dried for 7 days at 21.degree. C. and 65% relative humidity. For room temperature testing 1 cm by 5 cm test samples were prepared and mounted on a cardboard mount. The mounted specimen was clamped between a pair of jaws spaced 3 cm apart of an Instron apparatus and the jaws separated at 50 cm/min. Wet tests were performed on specimen dried films immersed in water at 21.degree. C. for 24 hours before mounting. PA1 Tests were performed over a range of temperatures by using an Instron environment cabinet. PA1 ii) The tensile strength/elongation tests on pigmented products were performed using procedure (i) but with a wet drawn down film of 0.25 mm thickness. PA1 iii) Water uptake: Dried (5 cm.times.5 cm) films of the emulsion or pigmented product were prepared as in methods (i) or (ii) and immersed in water at 21.degree. C. Water uptake was determined by weighing after 1 day and 7 days.
The copolymer will have a Tg in the range about 0.degree. C. to about -30.degree. C., preferably -5.degree. C. to -20.degree. C. The Tg is obtained within a suitable range by selection of the monomers and their content. Tg of a copolymer may be calculated from the monomer values or measured using Dynamic Mechanical Thermal Analysis (DMTA).
The solids contents of the emulsions will usually be in the range 35% to 70% by weight, preferably 45% to 60% to provide cost effective provision of the film forming solids.
The weight mean particle size of the emulsion particles will usually be in the range 0.5 to 3.0 microns as measured by using a Joyce Loebl disc centrifuge.
Although vinyl acetate is the preferred vinyl alkanoate monomer because of its availability, cost and known reactivity, other vinyl esters within the class defined are usable, in particular vinyl formate, propionate, butyrate and isobutyrate. The vinyl alkanoate monomer will be present at a level of about 10% to ensure the copolymer has the desired properties and amounts above about 60% are unlikely to be cost effective, preferably a level above about 40% will be used.
The preferred alkylene is ethylene but other ethylenic hydrocarbons, for example propylene butylene and isobutene are usable. Preferably the level is above about 15%.
The alkyl acrylate monomers are present to provide physical softening of the copolymers and are preferably present at a level above about 3% and below about 8%. The chain length of the alkyl group is preferably in the range 4 to 10. A preferred alkyl acrylate is 2-ethyl hexyl acrylate but butyl acrylate, hexyl acrylate and octyl acrylate are also satisfactory.
The vinyl esters of versatic acids are obtained from Shell Chemicals of Chester England under the Trade Mark "Veova". The preferred levels of vinyl versatates are from about 15% and to about 30% of the monomer composition. The presence of these monomers permits balancing of the polymer Tg and improves alkaline hydrolysis resistance.
The vinyl silane is preferably present at a level of up to about 2% for cost effectiveness. The vinyl silanes have the general formula CH.sub.2 .dbd.CH--Si(OX).sub.3 wherein X represents separately hydrogen, acyl, an unsubstituted alkyl radical or an alkoxy substituted alkyl radical with, at most, two of the X radicals being hydrogen. Examples of these silanes are vinyl triethoxy silane, vinyl trimethoxy silane, vinyl-tris (beta-methoxy ethoxy) silane and vinyl triacetoxy silane.
The presence of the alkyl acrylate and vinyl silane components together provide the desired balance between tensile strength and elongation, particularly at low temperatures.
Functional monomers may be included in the shell, for example monomers capable of hardening the total emulsion such as vinyl pivalate and dimethyl maleate. These hardening monomers may be present at a level of 0 to 20% by weight of the shell, with the desired characteristics being obtained at a cost/effective level usually in the range 5% to 10%. Hardening monomers may also be included in the core to provide the desired product features. Preferably the alkylene content of the shell is kept as low as possible.
Methods for preparing the copolymer emulsions of the invention are well characterised in the literature. Polymer synthesis (vols I and III) by Sandler & Karo (Academic Press 1974) and Preparative Methods of Polymer Chemistry (2nd Ed) by Sorenson and Campbell (Interscience 1968) provide preparative information. Methoden der Organischen Chemie (Houben-Wey) Band XIV published by George Thieme Verlag Stuttgart (1961) also provides preparative descriptions.
The copolymer emulsions of the invention are usable in paints intended for surface coatings; these compositions will usually comprise (by weight):
______________________________________ Pigmented compositions of use as roof treating compositions usually comprise (by weight of solids): ______________________________________ Thickener eg cellulose ether 1.5 to 3.5% Dispersant eg sodium polyphosphate 0.75 to 2.0% Preservative 0.05 to 0.2% Defoamer 0.1 to 0.3% Pigment 5 to 30% Filler 5 to 55% Coalescing solvent eg alcohol ester 1 to 3% Emulsion copolymer dry solids 3 to 35% Water, including emulsion remainder aqueous base ______________________________________
The fillers will include quartz powder, kaolin, silica and milled minerals; the pigments include titanium dioxide, zinc oxide and zinc sulphide.
The coatings formed by these compositions have water uptake level which allows response to changing weather conditions. A water uptake which is too high can lead to disintegration as the coating becomes spongy. At the other extreme a highly water resistant coating will not allow moisture between it and the substrate to escape with consequent damage from moisture retention or freezing.
These coatings will be applied by conventional means, for example, by spray, bush or roller. They are usable in protection or repair situations.
Test methods
The following procedures were used to test emulsions prepared according to the invention.
When reporting the elongation results the use of a + sign indicates the sample did not break at the maximum extension available with the machine at the test conditions.
Specific description of the invention
Copolymer emulsions were prepared to illustrate the invention.